Various abnormalities of the heart are generally treated by temporarily arresting the heart from beating, isolating the heart from systemic blood circulation, supporting the systemic blood circulation via an external cardiopulmonary bypass pump, and performing surgical operations directly on the stopped heart. This general method is herein referred to as a "cardiac bypass procedure". Examples of such cardiac bypass procedures include, without limitation: coronary artery bypass graft surgery ("CABG"); valve replacement surgery; cardiac transplantation surgery; and a procedure known as the "maze" procedure wherein conduction blocks are surgically formed in the wall of one or both of the atria in order to prevent atrial fibrillation.
Conventional techniques in performing such "cardiac bypass procedures" generally include cutting through the sternum in the chest cavity using well known "sternotomy" techniques, spreading open the rib cage, retracting the lungs from the region of the heart, and directly exposing the heart to the surgeon. One of various known cardioplegia agents may be used to temporarily arrest the heart from beating. Further to the bypass procedure, an external cross clamp is generally used to occlude the aorta in the region of the arch between the aortic root and the carotid arteries. With the cross-clamp in this position, both the left heart chambers and the coronary arteries into the heart are isolated from the systemic arterial circulation while the carotid arteries are fed with the blood flow from the bypass pump. In addition, flow from the superior and inferior vena cava is also temporarily diverted from the heart to the pump, usually by externally tying the vena caval walls onto venous pump cannulae.
Minimally Invasive Cardiac Bypass Catheter Systems
Recent advances have been made in the field of "cardiac bypass procedures" which include the use of novel catheter assemblies which are adapted to temporarily arrest and bypass the heart without the need for direct cross-clamping or externally tying the vena cavae. Such assemblies are generally herein referred to by the terms "minimally invasive catheter bypass systems," or derivatives of these terms, and generally include an arterial catheter, which isolates the left heart chambers from systemic arterial circulation beyond the aortic root, and a venous catheter, which isolates the right heart chambers from venous circulation from the vena cavae. Further to the intended meaning, such minimally invasive catheter bypass systems may be used during procedures which otherwise still require a sternotomy in an otherwise "open chest" or "open heart" procedure which directly exposes the heart, as well as during procedures which otherwise alleviate the need for such sternotomies, such as for example procedures known as "port access" procedures.
One particular example of a previously known "minimally invasive cardiac bypass system" uses an arterial catheter which occludes the aorta from systemic arterial circulation with an inflatable balloon located on the outside surface of the catheter's distal end portion which is positioned within the aorta. The arterial catheter further includes a cannula with lumens and distal ports which provide for cardioplegia agent delivery and venting of the left ventricle, respectively, while the heart is isolated from systemic circulation with the inflated balloon on the outer surface of the arterial catheter. Further to this known system, a venous catheter is further provided and uses a balloon in each of the superior and inferior vena cava. The venous catheter balloons inflate to occlude these great veins and thereby isolate the right heart chambers from systemic venous blood flow. Moreover, the venous and arterial catheters which combine to form minimally invasive cardiac bypass catheter systems engage to inlet and outlet ports, respectively of a cardiopulmonary bypass pump, which pump may be further considered a part of the overall system. One such known pump which is believed to be particularly usefull in cardiac bypass procedures, including minimally invasive bypass procedures, is known as the "BioPump", Model Number "BP80", which is available from Medtronic, Inc.
Further to the description for the minimally invasive cardiac bypass system example just provided above, the terms "proximal" and "distal" are herein used throughout this disclosure as relative terms. In the context of describing a device or catheter used in such a system, the term "proximal," such as in the phrase "proximal end", is herein intended to mean toward or closer to a user such as a physician, whereas the term "distal," such as in the phrase "distal end" is herein intended to mean away from or further away from the user. However, if and where the terms "proximal" and "distal" are herein used in the context of describing anatomical structures of the cardiovascular system or physiological blood flow, the term "proximal" is herein intended to mean toward or closer to the heart, whereas the term "distal" is herein intended to mean away from or further from the heart. Furthermore, the terms "upstream" and "downstream" are also relative terms which may be herein used interchangeably with "proximal" or "distal", respectively, in the anatomical or physiological context just described.
According to the method of using known minimally invasive cardiac bypass catheter systems such as the example summarized above, the heart is usually put on "partial bypass" prior to "complete bypass". The terms "partial bypass" are herein intended to mean a condition wherein the heart is beating and pumping blood throughout the body's circulation prior to inflating the balloons on the arterial and venous catheters, and wherein some blood is also aspirated from the vena cavae through the venous catheter, sent through the cardiopulmonary bypass pump, and infused into the arterial circulation through the flow ports along the arterial catheter. The terms "complete bypass" or "full bypass" or derivatives thereof are therefore herein intended to mean a condition wherein the heart is substantially isolated from systemic venous and arterial circulation by means provided by the venous and arterial catheters, respectively, such as for example by inflating balloons on the exterior surfaces of such venous and arterial catheters to thereby totally occlude the vena cavae and aorta, also respectively, as described above.
According to these definitions for partial and full bypass just provided, a patient is therefore put on partial bypass by first positioning the venous and arterial catheters at respectively predetermined locations along the vena cavae and aorta, respectively, such that the respective flow ports may provide for the respective aspiration or infusion of blood and such that balloons on the catheter outer surfaces may be thereafter inflated to isolate the right and left heart chambers, also respectively, during full bypass. The procedure for subsequently weaning a patient from partial bypass to full bypass according to the known minimally invasive cardiac bypass system example described above generally proceeds as follows.
Cardioplegia agent is delivered during partial bypass in order to begin reducing the cardiac function ultimately toward the temporarily arrested state. The external balloons are inflated to occlude the vena cavae and isolate the right heart from systemic venous circulation prior to inflating the arterial catheter's balloon to isolate the left heart from systemic arterial circulation. During this "weaning" period, the bypass pump circulates the blood aspirated from the vena cavae while the heart continues to pump a declining volume of residual blood from the coronary sinus, right heart chambers, pulmonary circulation (including lungs), and left heart chambers. As the residual volume of blood pumping through the heart declines, and as the cardiac function continues toward temporary arrest under cardioplegia effects, the balloon on the exterior surface of the arterial catheter is then inflated to occlude the aorta and finally achieve full or complete bypass.
Upon inflating the arterial balloon and totally occluding the aorta during the "weaning" period onto full bypass as just described, additional cardioplegia agent delivery continues distally of the inflated balloon. However, it has been observed that "back pressure" on the cardioplegia delivery cannula during cardioplegia agent delivery, together with the pressure from the beating heart against the totally occluded aorta, may push the arterial balloon downstream along the aorta. As a result, a user may be required to reposition the balloon at the initially desired location along the ascending aorta between the aortic root and the carotid arteries. It is believed that the repositioning of the arterial balloon in response to this pressure response may be performed while the balloon is inflated, or during subsequent iterations of positioning and then inflating in order to adjust for the observed post-inflation movement.
Still further to the known "minimally invasive cardiac bypass systems," weaning a patient off of "complete bypass" and off of the cardiopulmonary bypass pump while reestablishing physiological cardiac output generally requires deflation of the external balloon on the external surfaces of the arterial and venous catheters. However, some patients have been observed to present complications while cardiac function is being reestablished, which complications may require returning the patient back to a full bypass condition. Therefore, patients are generally kept in surgery for a prolonged period of time subsequent to deflating the balloons on the bypass system catheters and after reestablishing the cardiac function in order to observe the heart's recovery. In cases where such patients are required to be put back onto cardiac bypass, the balloons must be repositioned at their desired location and then reinflated to isolate the heart. Particularly regarding the occlusion balloon on the external surface of the arterial catheter, this reinflation while the heart is pumping may present the same repositioning issues as previously described above.
It is further believed that the arterial balloon repositioning which may be required during use of arterial catheters according to the known minimally invasive cardiac bypass systems may present a cumbersome and potentially dangerous detriment to the efficiency and safety of the overall minimally invasive cardiac bypass procedure.
There is a need for a minimally invasive cardiac bypass system which includes an arterial catheter with an external balloon which is adapted to inflate and engage the aortic wall to secure the catheter at a predetermined location along the ascending aorta between the aortic root and the carotid arteries along the aortic arch and which is further adapted such that the external balloon does not substantially reposition during such inflation while cardioplegia agent is being delivered to the heart through a cardioplegia cannula upstream from the external balloon or while the heart is beating such as when a patient is being weaned onto partial or full cardiac bypass.
There is also a need for a minimally invasive cardiac bypass system which includes an arterial catheter with an external balloon which is adapted to remain inflated and engaged to the aortic wall at a predetermined location along the ascending aorta while cardiac function is being reestablished as a patient is weaned off of a cardiopulmonary bypass pump subsequent to a surgical cardiac procedure.
There is also a need for a minimally invasive cardiac bypass system which includes an arterial catheter that is adapted to: anchor within the ascending aorta; shunt antegrade aortic blood flow from the aortic root, proximally through a flow lumen within the catheter past the anchor, and into the systemic arterial circulation downstream of the anchor while the heart is still beating during partial cardiac bypass; selectively occlude the shunted antegrade flow path, thereby isolating the aortic root from systemic circulation when the heart is temporarily arrested and on full cardiac bypass; and selectively provide a retrograde flow path through the internal flow lumen of the catheter for active infusion of oxygenated blood from a bypass pump and into the systemic arterial circulation proximally of the anchor when the heart is temporarily arrested during full cardiac bypass.
There is also a need for a minimally invasive cardiac bypass system which includes an arterial catheter which is adapted to shunt antegrade aortic blood flow before or during partial cardiac bypass from the aortic root, through a distal flow port into an internal flow lumen within the catheter, and out of the internal flow lumen through an intermediate flow port into systemic arterial circulation while minimizing hemolysis at the transition region between the aortic root and the distal flow port into the internal flow lumen and also while minimizing the movement of the arterial catheter.
There is also a need for a minimally invasive cardiopulmonary bypass system which includes a venous catheter which is adapted to substantially aspirate the venous blood from the vena cavae while substantially isolating the right ventricle from the vena caval blood flow without circumferentially engaging the interior wall of the inferior or superior vena cavae and without completely occluding the vena cavae.